In the field of mass spectrometry in order to introduce ions from ion source into mass analyzer at higher pressure (1˜104 Pa or 0.0075˜75 torrs), a high-frequency (or RF) guiding device is normally used. The effective potential barrier formed with the high frequency voltage applied on the electrodes in this device would accelerate ions towards the central axis for focusing. The ions will lose a large portion of their kinetic energy due to collisions with the neutral gas molecules, and hence ions would be confined in the vicinity of the central axis before passing through the aperture for differential pumping and entering into the lower pressure region of a mass spectrometer. This kind of RF focusing device has different variations including D. J. Douglas' initial invention of the multi-pole guide system (U.S. Pat. No. 5,179,278), R. D. Smith's ion funnel (U.S. Pat. No. 6,107,628), N. Inatsugu, H. Waki's Q-array device (U.S. Pat. No. 6,462,338B1), and Bateman's (U.S. Pat. No. 7,095,013) travelling wave ion guide. However, as the first ion guide right after the ion source, it would experience very strong gas flow induced by the pressure difference. Sometimes the effect of the gas flow on the ions is even stronger than that of the electric field. In such case, the electrodes themselves, or their mounting brackets often inevitably interfere with the gas flow. In addition, the effect of the position of the pipes on pumping may also cause turbulence or flow jitter on the ion path, and further affect the transmission of the ions.
In the U.S. Pat. No. 5,572,035, the inventor Franzen has proposed to use wire electrodes to form ion reflector in order to confine ions. This reflector design can theoretically have good transmission for gas molecules. But generally the meshes are very soft, and the inventor did not give an example of how to securely install them at a specific location without effects from the air flow. If mounted with additional brackets, the additional brackets will also affect the direction of the gas flow. In U.S. Pat. No. 7,391,021, they raise a structure to confine ions in a serial set of stacked RF diaphragm, but the slimsy diaphragms are still with high risk to be shape-changed under high flow rate toward its axis.
In addition, in the ion guiding devices developed in the past, the opposite phases of the high frequency voltages applied on adjacent electrodes (either parallel to each other (between lines or between surfaces), or being concentric rings or arcs) would create very large capacitance between electrodes. For example, U.S. Pat. No. 6,107,628 described an ion funnel design using sheet electrodes for applying voltages with opposite polarity. Similar structure was also introduced in U.S. Pat. No. 7,595,486's RF multipole design. Two groups of adjacent wires with opposite phase RF superimposed are placed all parallel to shape a pole rod surface for confining the ions inside.
In these design, the power consumption of the power supply is very large due to the large capacitance caused by the multiple parallel layers (this is equivalent to many parallel capacitors for the high frequency power supply).
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.